Flow meters for public use are required in many countries to meet specified accuracy standards.
In the United Kingdom the relevant British Standard 5728 (amendment 1-1985) Class D requires domestic water meters to record from a starting flow rate of 0.00375 cubic meters per hour; to respond to a minimum flow rate of 0.0075 cubic meters per hour, and above which accuracy is to be within +/-5%; through a transition flow rate 0.0115 cubic meters per hour above which the accuracy is to be within +/-2%, to a maximum flow rate of 2.0 cubic meters per hour. Turndown (the ratio between the maximum and minimum flow rates to be recorded) is thus 267:1.
The specified U.K. pressure drop is to be no more than 0.25 bar at the nominal flow rate, and no more than 1.0 bar at the maximum flow rate.
The U.K. domestic water pipework is of internal diameter 15 mm +/-1 mm, so that at minimum and maximum flow rates the mean water velocities are 0.012 m/s and 3.14 m/s; since the corresponding Reynolds numbers at ambient conditions are 135 and 36,000 the flow goes from laminar to turbulent over the flow range.
A water meter suitable for widespread industrial and domestic fitting could lead to a substantial reduction in water demand as users become more careful to control waste, with a reduction in the facilities needed by the water authorities for processing and storage.